Electrician's Licensing Practice Exam

Which of the following is not a conductor?

1. Gold

2. Water

3. Silver

4. Air

The correct answer is: Air

Air is not a conductor because it is an insulator under normal conditions. Conductors are materials that allow electric current to flow freely due to the presence of free electrons. Metals like gold and silver are excellent conductors because they have a high density of free electrons, making them highly efficient in conducting electricity. Water, while not a perfect conductor, can conduct electricity due to the presence of dissolved ions. Pure water is actually a very poor conductor, but when impurities such as salts are present, it becomes much more conductive. In contrast, air does not have free electrons or ions in significant amounts under standard atmospheric conditions, which prevents it from conducting electricity effectively. This is why air is typically utilized as an insulator in various electrical applications, such as in the spacing of conductors in overhead power lines.